Subsurface safety valves are well known in the art. They are used in a well, such as an oil or gas well, to provide a safety shut off in the event of a well failure. A subsurface safety valve is typically mounted with other components, such as production tubing, and is set downhole in the well. The valve is typically a normally closed valve, in that the valve automatically shuts off under default conditions, such as with no power. When shut, the safety valve does not allow contents from below the safety valve, such as production fluids, to continue flowing to the surface of the well. Uncontrolled flowing production fluid, such as gas or other hydrocarbons, could cause explosions or otherwise damage the above-ground facilities in the event of a well failure.
Typically, a valve element, such as a disk-shaped “flapper”, is used to seal off the production fluid in a main bore of the safety valve. The flapper is mounted to a hinge and can be pivoted to an open position to allow production fluid to flow. The flapper is forced open by a flow tube mounted in a bore of the subsurface safety valve. The flow tube slidably engages the flapper as the flow tube moves down the bore and pushes the flapper out of the main bore flow path. In many designs, an actuator having a piston in a side chamber adjacent the main bore is remotely actuated to cause the flow tube to move down to engage the flapper and force the flapper out of the flow path. A spring connected to the flow tube is commonly used separately or in conjunction with the piston to force the flow tube up to allow the flapper to enter and close off the main bore.
The challenge in a typical subsurface safety valve design is sealing. For example, seals that seal the piston as it travels up and down the side chamber can be exposed to debris and other well substances. The debris can cut or otherwise interfere with the seals. Further, the typical engagement of a piston to a flow tube can cause the piston to be nonuniformly loaded and cause misalignment of the piston. The misaligned piston can nonuniformly contact mating surfaces and reduce sealing effectiveness.
Some designs have attempted to correct this problem by supplementing the piston seals with secondary seals. As the piston reaches a maximum downward travel, a rod connected to the piston can be seated to help reduce the flow of debris and other leakage into the area that the piston would otherwise travel. Similarly, the piston or rod connected thereto can be sealed at an upward limit of the piston travel with an additional secondary seal. However, such secondary seals still encounter difficulties in effective sealing. These difficulties are also encountered in other types of subsurface valves, including without limitation, subsurface flow control valves and other downhole valves.
The field of subsurface valves is a mature art. Small, incremental improvements can make a substantial difference in performance. The present invention offers a solution to the above sealing ineffectiveness by providing an improved sealing system for the piston and associated members.